Any Mod's For Dual Field PI's Chatty Threshold?

[Sand Hunter]

I just picked up my first PI, White's Dual Field, after swinging VLF's, a TR & a BFO for the last 56 years.

Lots of guys say that the DF's threshold is chatty, even a bit like static, but the TDI Beach Hunter's threshold is smooth, and the Surf PI & PI Pro's thresholds were smooth, so wondering why in the middle of that pack, the Dual Field has a chatty threshold tone?

Anyone know of a mod that can smooth out the Dual Fields threshold tone, to make it smooth like the other White's PI's?

[GB_Amateur]

20 hours ago, Sand Hunter said:

Lots of guys say that the DF's threshold is chatty, even a bit like static, but the TDI Beach Hunter's threshold is smooth, and the Surf PI & PI Pro's thresholds were smooth, so wondering why in the middle of that pack, the Dual Field has a chatty threshold tone?

Well 20 hrs in and no response so I'll take a crack.  (Warning:  this isn't my area of expertise.)  In general, PI's made for salt water detecting and PI's made for dry land detecting have different ground balancing characteristics.  One type of ground is conductive (salt water and wet salt sand) whereas the other is primarily magnetic (magnetite and other ferromagnetic minerals).  Some detectors will handle both types of ground.

If you look at Steve's database descriptions of these White's PI's (I could not find the Surf PI & PI Pro, but the other two are there) you will see that the Surfmaster PI Dual Field has "Automatic Ground Rejection" whereas the TDI BeachHunter has "Full Control Ground-Balance".  That full control allows you to turn off the ground balance if not in magnetic ground, which is a nice plus.

I have a TDI SPP which is basically a TDI/SL without delay control nor a conductivity switch.  But it does share the ground control circuitry with the TDI BeachHunter.  If I turn off ground balance the threshold tone is rock steady.  When ground balance is on the threshold is warbly.  Since the Surfmaster PI Dual Field doesn't have any external control for ground balance, you can't turn it off.

As far as whether the Surfmaster PI Dual Field can be modified, maybe Carl Moreland ( @Geotech ) who I'm pretty sure was involved with some of White's TDI development can help you there.  In the least he can correct anything I said wrong above.  😅

[Geotech]

The SMPI does not have GB at all, it is similar to a TDI with GB turned off. There is nothing inherent in the DF coil that would make it noisier than a mono coil so I don't know what might be going on.

[sonnar28]

I think some of the noisy threshold comes from the machine rapidly switching input from the small inner coil to the large outer coil. I had the dual field coil on mine swapped out to a 14" Miner John mono coil, which settled things down some, but not as much as you might expect.

Adding a clip on ferrite core to the coil wire usually helps some with the chatter, just don't go for a really tight fit or it can cut into the wire insulation. I just used black electrical tape wrapped under the core to keep it stationary.

Charles

[Geotech]

13 hours ago, sonnar28 said:

I think some of the noisy threshold comes from the machine rapidly switching input from the small inner coil to the large outer coil.

It doesn't work that way. The coils are wired in series and behave exactly the same a single mono coil.

https://patents.google.com/patent/US7994789

[Furmiston]

23 hours ago, Geotech said:

It doesn't work that way. The coils are wired in series and behave exactly the same a single mono coil.

https://patents.google.com/patent/US7994789

Hi Geotech, I have the tdi sl with a 16volts battery, which I use solely with the stock coil, you kindly answered a question concerning voltage and resistance of different coils. I also have the tdi pro that has the warbly threshold , as I only beach hunt the stable threshold of the sl is great for those deep faint signals. I’ve read that you designed the sl. I understand this has been talked about before, but could I ask what makes the threshold so stable on the sl.

 

[Geotech]

It was the cumulative effect of several things: better opamps, elimination of some extraneous circuitry, a modified integrator, and better rebound clamping.

[Furmiston]

44 minutes ago, Geotech said:

It was the cumulative effect of several things: better opamps, elimination of some extraneous circuitry, a modified integrator, and better rebound clamping.

Thanks Geotech for the reply, I’ve found some amazing things with the sl and I’ve used various pulse detectors on the beach but it’s still my favourite. 
I’d love to see a revamped version with more power and to be able to safely use lager coils. 
could I ask your opinion on the whites 12 inch oz mono compared to the 12 inch duel field. Does one detect deeper than the other?. Not that I have the oz mono, they seem quite rare.

[Geotech]

The DF is a 50/50 compromise between a 6" coil and a 12" coil. So a mono 6" mono coil will be more sensitive to tiny targets and a 12" mono coil will go deeper on larger targets. But not by a whole lot, either way.